Chemical-mechanical polishing device, damascene wiring forming device, and dama-scene wiring forming method

ABSTRACT

In a chemical mechanical polishing apparatus in accordance with the present invention, a material having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm is used as an elastic member ( 16 ) arranged between a polishing pad ( 12 ) and a platen ( 36 ). Therefore, both flatness and uniformity of a wafer can be sufficiently improved.

TECHNICAL FIELD

[0001] The present invention relates to a polishing apparatus and apolishing method in which a metal film surface formed on a semiconductorsubstrate is polished by a chemical mechanical approach.

BACKGROUND ART

[0002] A planarizaion process of a wafer (semiconductor substrate) in amanufacturing process is important to attain a higher integration of asemiconductor device. A CMP (Chemical Mechanical Polishing) apparatus iswidely used as an apparatus planarizing a wafer. In a CMP apparatus, forexample, while polishing slurry is supplied to a wafer to be polished, ametal film and the like on the wafer are polished by contact with apolishing pad.

[0003] Now, in order to selectively polish protruding portions (improveflatness) of an insulating film, a metal film and the like on a wafer,deformation of a polishing pad surface needs to be suppressed and a highhardness of the polishing pad is required. On the other hand, in orderto perform uniform polishing on the entire semiconductor wafer (improveuniformity), flexibility sufficient to conform warp of the wafer isrequired for the polishing pad. Therefore, since there is a trade-offbetween flatness and uniformity in selecting a polishing pad, it isdifficult to ensure both flatness and uniformity of polishing. Thus, forthe purpose of improving both flatness and uniformity of the wafer, sucha polishing pad is employed that has a two-layer structure formed with ahard material arranged in an upper layer in contact with the wafer to bepolished and a soft material arranged in a lower layer thereof.

[0004] A wafer holding (fixing) method will now be described. Generally,in a CMP apparatus, a wafer is held using a vacuum chuck (vacuumsuction), a backing film (backing pad) and the like. Advantages of usinga vacuum chuck include: easiness of wafer replacement (attachment andremoval); secure and firm holding of wafer; and elimination of waferwarp. As a disadvantage, the use of the aforementioned polishing padhaving the two-layer structure described above cannot accommodatemacroscopic thickness variations of the wafer, resulting in a poorpolishing uniformity.

[0005] On the other hand, although the use of a backing pad is inferiorin easiness of wafer attachment and removal and secure holding of wafer,it has an advantage in that wafer warp, thickness variations and thelike can be accommodated (reduced) to some extent as the backing paditself has a good elasticity. As a result, macroscopic undulations ofthe wafer can be reduced to some extent and poorer polishing uniformitycan be prevented to some extent. Therefore, holding a wafer using abacking pad is presently common. A polishing apparatus using a backingpad as wafer holding means and using a polishing pad having theaforementioned two-layer structure (hard material and soft material) isdisclosed for example in Japanese Patent Laying-Open Nos. 10-138123,9-321001, 9-260318, 7-266219 and 7-297195.

[0006] The present situation of the conventional polishing method hasbeen described above. In conclusion, the conventional CMP apparatuscannot improve both flatness and uniformity in a wafer sufficiently.This problem is outstanding particularly in case of polishing adamascene structure.

DISCLOSURE OF THE INVENTION

[0007] The present invention is made in view of the situation describedabove. A first object of the present invention is to provide a chemicalmechanical polishing apparatus capable of sufficiently improving bothflatness and uniformity of polishing even with a vacuum chuck excellentin easiness of wafer attachment and removal and secure holding of awafer.

[0008] A second object of the present invention is to provide adamascene interconnection forming apparatus and method in which anaccurate damascene interconnection can be formed by using a polishingapparatus realizing good flatness and uniformity.

[0009] In order to achieve the above objects, a chemical mechanicalpolishing apparatus in accordance with the present invention is appliedto an apparatus including: a substrate holding table holding asemiconductor substrate by vacuum suction; a polishing pad being incontact with the semiconductor substrate; a platen holding the polishingpad; and an elastic member arranged between the polishing pad and theplaten. It is characterized in that a material having a hardness definedby JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm isused as the elastic member.

[0010] A damascene interconnection forming apparatus in accordance withthe present invention is applied to a damascene interconnection formingapparatus forming an insulating film on a semiconductor substrate,forming a recessed portion in a prescribed region of the insulatingfilm, forming a barrier metal film on a surface of the insulating filmincluding the recessed portion, and forming a metal interconnection filmon the barrier metal film to completely fill in at least the recessedportion, followed by polishing the metal film and the barrier metal filmuntil the insulating film is exposed in a region other than the recessedportion. It is characterized by including: first polishing means forperforming a first polishing step of polishing the metal interconnectionfilm until the barrier metal film is exposed in the region other thanthe recessed portion; and second polishing means for performing a secondpolishing step of polishing the barrier metal film until the insulatingfilm is exposed in the region other than the recessed portion.Furthermore, the first polishing means includes: a substrate holdingtable holding the semiconductor substrate by vacuum suction; a polishingpad being in contact with the semiconductor substrate; a platen holdingthe polishing pad; and an elastic member arranged between the polishingpad and the platen and having a hardness defined by JIS standard K6301(A type) of 10-40 and a thickness of 5-30 mm. In addition, the secondpolishing means includes: a substrate holding table holding thesemiconductor substrate by vacuum suction; a polishing pad being incontact with the semiconductor substrate; a platen holding the polishingpad; and an elastic member arranged between the polishing pad and theplaten and having a hardness defined by JIS standard K6301 (A type) ofat least 50.

[0011] A damascene interconnection forming method in accordance with thepresent invention is applied to a damascene interconnection formingmethod of forming an insulating film on a semiconductor substrate,forming a recessed portion in a prescribed region of the insulatingfilm, forming a barrier metal film on a surface of the insulating filmincluding the recessed portion, and forming a metal interconnection filmon the barrier metal film to completely fill in at least the recessedportion, followed by polishing the metal film and the barrier metal filmuntil the insulating film is exposed in a region other than the recessedportion. It is characterized by including: a first polishing step ofpolishing the metal interconnection film until the barrier metal film isexposed in the region other than the recessed portion using firstpolishing means; and a second polishing step of polishing the barriermetal film until the insulating film is exposed in the region other thanthe recessed portion using second polishing means. Furthermore, thefirst polishing means includes: a substrate holding table holding thesemiconductor substrate by vacuum suction; a polishing pad being incontact with the semiconductor substrate; a platen holding the polishingpad; and an elastic member arranged between the polishing pad and theplaten and having a hardness defined by JIS standard K6301 (A type) of10-40 and a thickness of 5-30 mm. In addition, the second polishingmeans includes: a substrate holding table holding the semiconductorsubstrate by vacuum suction; a polishing pad being in contact with thesemiconductor substrate; a platen holding the polishing pad; and anelastic member arranged between the polishing pad and the platen andhaving a hardness defined by JIS standard K6301 (A type) of at least 50.

[0012] In the damascene interconnection forming apparatus and methoddescribed above, preferably, the first polishing means and the secondpolishing means are implemented by a single chemical mechanicalpolishing apparatus. More specifically, the polishing apparatusincludes: a substrate holding table holding the semiconductor substrateby vacuum suction; first and second platens arranged in positionsopposing the substrate holding table in a polishing operation; a firstpolishing pad arranged on the first platen; a second polishing padarranged on the second platen; a first elastic member arranged betweenthe first platen and the first polishing pad and having a hardnessdefined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30mm; and a second elastic member arranged between the second platen andthe second polishing pad and having a hardness defined by JIS standardK6301 (A type) of at least 50. In performing the first polishing step,the substrate holding table is arranged in a position opposing the firstplaten, and in performing the second polishing step, the substrateholding table is arranged in a position opposing the second platen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a side view (with a partial cross section) showing aconfiguration of a CMP apparatus in accordance with the presentinvention with a polishing pad fixed by a mounting technique.

[0014]FIG. 2 is a cross sectional view showing a configuration of a mainpart of the CMP apparatus in accordance with the present invention withthe polishing pad adhesively fixed to a platen.

[0015]FIGS. 3A to 3C are cross sectional views showing the steps of adamascene interconnection forming method in accordance with the presentinvention, in which FIG. 3A is a state before polishing, FIG. 3B is astate after a first polishing step and FIG. 3C is a state after a secondpolishing step.

[0016]FIG. 4 is an illustration showing points for measuringwithin-wafer-surface-uniformity (polishing uniformity) in accordancewith the present invention.

[0017]FIG. 5 is a plane view showing a configuration of a main part of apolishing apparatus (a platen and a wafer holding table) in accordancewith the present invention.

[0018]FIG. 6 is a side view of the apparatus shown in FIG. 5 with apartial cross section.

[0019]FIG. 7 is a plane view showing the configuration of the main partof another type of polishing apparatus (the platen and the wafer holdingtable) in accordance with the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

[0020] The present invention is applied to a case where a metalinterconnection layer having a narrow width (less than 200 μm) of arecessed portion is polished, in a type of CMP apparatus in which awafer is basically fixed by a vacuum chuck.

[0021]FIG. 1 shows a configuration of a CMP apparatus according to afirst embodiment of the present invention. This CMP apparatus includes apolishing pad 12 in contact with a wafer 10 to be polished, a platen 14with polishing pad 12 attached thereto, an elastic member 16 arrangedbetween polishing pad 12 and platen 14, a wafer stage 20 holding wafer10, a retainer 18 fixed on wafer stage 20, and a wafer turn table 22rotatably supporting wafer stage 20. The main feature of the presentinvention is in a setting of hardness and thickness of elastic member16. It is noted that a specific setting value of elastic member 16 willbe described later.

[0022] Elastic member 16 is formed like a ring (doughnut-shaped) havinga hole at the center thereof and fixed on platen 14 by a double-facedtape and the like. Elastic member 16 is set on platen 14 withoutletting-in air therebetween. Normally, once elastic member 16 is set onplaten 14, it is not frequently replaced. Polishing pad 12 is alsoformed like a ring (doughnut-shaped) and fixed on a bottom face ofplaten 14 by an inner ring 24, an outer peripheral ring 26 and bolts 28,30.

[0023] Wafer stage 20 is provided in a rotatable manner on wafer turntable 22. Retainer 18 is fixed on wafer stage 20 and wafer 10 is fixedon wafer stage 20 by a vacuum chuck. Platen 14, wafer turn table 22 andwafer stage 20 each are rotated about axes A-A′, B-B′ and C-C′. At thecenter of platen 14, a slurry supply hole 32 is provided to extendvertically, and prescribed slurry is supplied from this slurry supplyhole 32 during a polishing operation.

[0024] Polishing pad 12 is fixed on platen 14 by a so-called mountingtechnique. Specifically, without using adhesive and the like, it isfixed by fastening the aforementioned bolts 28 and 30 only at an outerperipheral portion and an inner peripheral portion. It is noted that inthe present invention a method of fixing a polishing pad is not limitedto the mounting technique and a variety of techniques including anadhesive technique (FIG. 2) and the like can be employed.

[0025] In a polishing operation, wafer 10 is fixed on wafer stage 20 bya vacuum chuck, and platen 14, wafer turn table 22 and wafer stage 20each are driven to rotate. Thereafter, while slurry is supplied fromslurry supply hole 32, platen 14 is brought down and polishing pad 12 ispressed against a polished surface of wafer 10 at a prescribed pressurefor polishing.

[0026]FIG. 2 shows an example in which a polishing pad is adhesivelyfixed on a platen. In this example, an elastic member 38 is adhesivelyfixed on a platen 36, and a polishing pad 40 is adhesively fixed onelastic member 38. Wafer 10 is fixed on a bottom surface of waferholding table 42 by vacuum suction. Inside wafer holding table 42, aplurality of holes 44 for evacuation are formed.

[0027] Elastic member 16, 38 in accordance with the present invention isset to have a thickness defined by JIS standard K6301 (A type) of 10-40and a thickness of 5-30 mm. In the following, grounds for this(experimental data) will be described. It is noted that such a polishingpad can be used that has a hardness defined by JIS standard K6301 (Atype) of 90 or more and a thickness of 0.5-2 mm. In the experimentbelow, IC1000 manufactured by Rodel Inc. in USA (having a hardness of 95and a thickness of about 1.3 mm) was used.

[0028] 1. Evaluation for Hardness of the Elastic Member

[0029] An experiment was performed on changes of flatness and uniformityin wafer polishing with respect to the hardness of elastic member 16 or38. The experiment was performed on a sample (wafer) shown in FIG. 3A.The wafer had a pattern by forming a thermal oxide film (insulatingfilm) 46 having a thickness of 5000 Å on a substrate, forming a recessedportion having a width of 10 μm-5 mm and a depth of 4500 Å (to be aninterconnection portion after completing polishing) in a prescribedregion, forming a Ta film (barrier metal film) 48 thereon having athickness of 200 Å, forming a Cu seed film 50 thereon having a thicknessof 1000 Å, and further forming Cu plating 52 (metal interconnectionfilm) thereon having a thickness of 1 μm. The pattern used in theexperiment had a line and space of a 10 mm length with a space set at 5mm. The lines (recessed portions) as used herein had different widths(10 μm-5 mm). The thickness of the elastic body was 10 mm. Furthermore,a polishing rate was set at a value of 6000 Å/min when an entirely flatfilm (mat film) of Cu was polished at a pressure of 300 g/cm².

[0030] (1) Flatness Evaluation

[0031] In a flatness evaluation, polishing (in one step) was performeduntil oxide film 46 in the aforementioned pattern surface was exposed,and an interconnection thickness decreasing amount (dishing) afterpolishing was measured in the interconnection portions having a varietyof widths. The experimental results are shown in Table 1. It is notedthat in the table the hardness is a value defined by JIS standard K6301(A type) and dishing amount is expressed in A. Furthermore, in thetable, “IC1000/400” means IC1000/400 manufactured by Rodel Inc. in USA.This is a polishing pad with two-layer structure conventionally commonlyused, using IC1000 (having a hardness of 95 in conformity withJIS-K6301) as a hard material of an upper layer (corresponding to thepolishing pad of the present invention) and using SUBA400 (having ahardness of 55-66 in conformity with JIS-K6301) as a soft material of alower layer (corresponding to the elastic member of the presentinvention). TABLE 1 interconnection width hardness 10 μm 20 50 100 200500 1 mm 2 mm 5 mm 5 200 400 800 1700 2000 3500 3800 4000 4500 10 50 100100 300 600 1800 2000 3200 4500 20 50 100 100 300 500 1500 1700 18004500 40 50 100 100 300 500 1300 1500 1700 4500 60 50 100 100 300 5001200 1300 1500 4500 IC 1000/400 50 100 100 300 400 1100 1200 1400 3500

[0032] As is clear from the Table 1 above, good flatness (low dishingamount) is obtained when a hardness is 10 or more. It is noted that in acase where an interconnection width (that is, a width of the recessedportion formed in insulating film 46) is 500 μm or more even with ahardness of 10 or more, flatness is deteriorated. This is not asignificant problem, however, since an actual width of the metalinterconnection layer is not more than 200 μm.

[0033] (2) Uniformity Evaluation

[0034] Polishing uniformity within a wafer surface was determined withelastic member 16 or 38 having a hardness defined by JIS standard K6301(A type) between 5 and 90. As indicated by × in FIG. 4, determination ofuniformity “δ” was performed by measuring a film thickness X_(i) attwenty-five points on two straight lines intersecting through the centerof wafer 53, based on the following equations.

[0035] Film thickness: X_(i) (i=1-25)

[0036] Average film thickness: X={fraction (1/25)}·ΣX_(i)

[0037] Within-wafer-surface-uniformity: δ=1/X·{square root}{square rootover ( )}({fraction (1/25)}·Σ(X−X_(i))²)×100

[0038] The experimental results are shown in Table 2. TABLE 2 hardness 510 20 40 60 90 IC 1000/400 uniformity 5.3 3.8 3.5 3.7 10.8 15.3 20.4

[0039] As is clear from the table above, good uniformity is obtainedwhen a hardness of elastic member 16, 38 is between 5 and 40,particularly between 10 and 40.

[0040] 2. Evaluation for the Thickness of the Elastic Member

[0041] An experiment was performed on changes of flatness and uniformityin wafer polishing with respect to the thickness of elastic member 16 or38. Similar to the case of the hardness of the elastic member, theexperiment was performed on a sample (wafer) shown in FIG. 3A.

[0042] (1) Flatness Evaluation

[0043] In a flatness evaluation, polishing (in one step) was performeduntil oxide film 46 in the aforementioned pattern surface was exposedand an interconnection thickness decreasing amount (dishing) afterpolishing was measured in an interconnection portion having a width of200 μm. The experimental results are shown in Table 3 in a range of athickness of 3 mm-60 mm and a hardness of 10-40. It is noted that in thetable, the hardness is a value defined by JIS standard K6301 (A type)and a dishing amount is expressed in Å. TABLE 3 thickness hardness 3 mm5 10 20 30 40 60 10 600 600 600 600 900 1300 20 500 500 500 500 500 8001100 40 500 500 500 500 800 1000

[0044] As is clear from Table 3, good flatness is obtained when elasticmember 16 or 38 has a thickness of not less than 3 mm and not more than30 mm.

[0045] (2) Evaluation for Within-Wafer-Surface-Uniformity

[0046] The experiment on a uniformity evaluation was performed in thesame condition as that of the flatness described above. Specifically,polishing (in one step) was performed until oxide film 46 in the patternsurface was exposed, and uniformity after polishing in theinterconnection portion having a width of 20 μm was measured. Theexperimental results are shown in Table 4 in a range of a thickness of 3mm-60 mm and a hardness of 10-40. It is noted that determination ofuniformity “δ” was performed by measuring film thickness X_(i) attwenty-five points on two straight lines intersecting through the centerof wafer 53 (FIG. 4), based on the following equations.

[0047] Film thickness: X_(i) (i=1-25)

[0048] Average film thickness: X={fraction (1/25)}·ΣX_(i)

[0049] Within-wafer-surface-uniformity: δ=1/X·{square root}{square rootover ( )}({fraction (1/25)}·Σ(X−X_(i))²)×100

[0050] TABLE 4 thickness hardness 3 mm 5 10 20 30 40 60 10 6.8 4.2 3.84.8 5.2 7.6 20 10.8 4.5 3.5 3.5 3.2 4.7 6.2 40 12.3 4.7 3.7 3.1 5.3 7.5

[0051] As is clear from Table 4, good uniformity is obtained whenelastic member 16 or 38 has a thickness of not less than 5 mm and notmore than 30 mm.

[0052] Considering the experimental results shown in Tables 1 to 4 onthe whole, good flatness and uniformity is obtained when elastic member16 or 38 has a hardness of 10-40 (JIS standard K6301 A type) and athickness of 5 mm-30 mm.

[0053] Next, another embodiment of the present invention will bedescribed. In this embodiment, polishing of the damasceneinterconnection layer is performed in two steps. Specifically, polishingis performed until Ta film 48 is exposed in a first step and polishingis performed until oxide film 46 is exposed in a second step.

[0054] Flatness evaluation (experimental) results are shown in Table 5in a case where the damascene interconnection layer is polished in twosteps. In this experiment, in the first polishing step, elastic member16 or 38 for use had a hardness of 10 and 20 and a thickness of 10 mm,and other conditions were similar to those in the embodiment above (theexample using one step for polishing). In the second polishing step,IC1000/400 manufactured by Rodel Inc. in USA was used as the polishingpad, and the same slurry as in the first polishing step and differentslurry (having a selective ratio between Cu and Ta lower than that ofthe first polishing step) were used. Here, IC1000/400 manufactured byRodel Inc. in USA means that IC1000 (a hardness of 95 in compliance withJIS-K6301) is used as a hard material of an upper layer (correspondingto the polishing pad) and SUBA400 (a hardness of 55-66 in compliancewith JIS-K6301) is used as a soft material of a lower layer(corresponding to the elastic member).

[0055] In a flatness evaluation, an interconnection thickness decreasingamount (dishing) after polishing in the interconnection portion having awidth of 200 μm was measured. In the experiment, the hardness of theelastic member (16 or 38) for use in the first polishing step was set at10, 20. Furthermore, data (the experimental data in one step asdescribed above) is shown as a comparative example where polishing ofthe damascene interconnection layer (FIGS. 3A-3C) was performed in onestep. It is noted that in Table 5, the hardness is a value defined byJIS standard K6301 (A type) and a dishing amount is expressed in Å.TABLE 5 elastic body for first step slurry 10 20 IC 1000/400 same infirst and second steps 400 400 — different between first and secondsteps 300 300 — comparative example (only first step) 600 500 400

[0056] As is clear from Table 5, polishing in two steps (a firstpolishing step and a second polishing step) improves the flatness ascompared with polishing up to the oxide film in one step. Usingdifferent slurry between a first polishing step and a second polishingstep further improves the flatness.

[0057]FIGS. 5 and 6 show a configuration of a main part of a CMPapparatus (a platen and a wafer holding member) used to polish adamascene interconnection layer in two steps (a first polishing step anda second polishing step). FIG. 5 is a plane view and FIG. 6 is a sideview (with a partial cross section). In this embodiment, two differentplatens 54 and 56 are used to polish the damascene interconnection. Afirst platen 54 holds a first polishing pad 62. A first elastic member58 is arranged between first platen 54 and polishing pad 62. A secondplaten 56 holds a second polishing pad 64. A second elastic member 60 isarranged between second platen 56 and polishing pad 64.

[0058] It is noted that for the purpose of using terms consistently, incase of a polishing pad having a two-layer structure such as IC1000/400manufactured by Rodel Inc. in USA used in the experiment describedabove, an upper layer formed of a hard material being in contact with awafer to be polished will be referred to as “polishing pad” and a lowerlayer formed of a soft material positioned between the upper layer andthe platen will be referred to as “elastic member”. Furthermore, firstpolishing pad 62 and second polishing pad 64 can be used each having ahardness defined by JIS standard K6301 (A type) of not less than 90 anda thickness of 0.5 mm-2 mm. For example, IC1000 manufactured by RodelInc. in USA can be used as polishing pad 62, 64.

[0059] The CMP apparatus shown in FIGS. 5 and 6 is provided with asingle wafer holding table 66, and a wafer 68 is hold by vacuum suction.Wafer holding table 66 can be moved between a position opposing firstplaten 54 and a position opposing second platen 56 by a robot arm 70.

[0060] First platen 54 is used in the first polishing step (polishinguntil barrier metal 48 is exposed), and first elastic member 58 for usehas a hardness defined by JIS standard K6301 (A type) of 10-40 and athickness of 5-30 mm. On the other hand, second platen 56 is used in thesecond polishing step (polishing until oxide film 46 is exposed), andsecond elastic member 60 for use has a hardness defined by JIS standardK6301 (A type) of not less than 50.

[0061] In the CMP apparatus shown in FIGS. 5 and 6, in a case wherepolishing is performed on the damascene interconnection structure shownin FIGS. 3A-3C, wafer holding table 66 is arranged in a positionopposing (directly above) first platen 54 by operating robot arm 70, andas shown in FIG. 3B, Cu film 52 and Cu seed film 50 are polished untilTa film 48 is exposed (the first polishing step). Next, wafer holdingtable 66 is arranged in a position opposing (directly above) secondplaten 54 by operating robot arm 70, and as shown in FIG. 3C, Ta film 48is polished until thermal oxide film pattern 46 is exposed (the secondpolishing step).

[0062]FIG. 7 shows another example of the CMP apparatus (the platens andthe wafer holding members) used to polish the damascene interconnectionlayer (FIGS. 3A-3C) in two steps (a first polishing step and a secondpolishing step). In this example, a single, first platen 72 for use inthe first polishing step and two, second platens 74 and 76 for use inthe second polishing step are provided to polish the damasceneinterconnection. First platen 72 holds first polishing pad 62 and allowstwo wafers to be polished at the same time. First elastic member 58 isarranged between first platen 72 and polishing pad 62. Each secondplaten 74, 76 has second polishing pad 64. Second elastic member 60 isarranged between second platen 74, 76 and polishing pad 64.

[0063] In the CMP apparatus shown in FIG. 7, two, second platens 74 and76 are respectively provided with wafer holding tables 82 and 84, andthe wafer is held by vacuum suction. Wafer holding table 82 can be movedbetween a position opposing first platen 72 and a position opposingsecond platen 74 by a robot arm 78. Furthermore, wafer holding table 84can be moved between a position opposing first platen 72 and a positionopposing second platen 76 by a robot arm 80.

[0064] First platen 72 is used in the first polishing step (polishinguntil the barrier metal is exposed) and has a structure shown in FIG. 2.Specifically, first elastic member 38 is interposed between polishingpad 40 and platen 36. Furthermore, the elastic member for use has ahardness defined by JIS standard K6301 (A type) of 10-40 and a thicknessof 5-30 mm. On the other hand, second platen 74 is used in the secondpolishing step (polishing until the oxide film is exposed), and thesecond elastic member for use has a hardness defined by JIS standardK6301 (A type) of not less than 50.

[0065] In the CMP apparatus shown in FIG. 7, in a case where thedamascene structure shown in FIGS. 3A-3C is polished, wafer holdingtables 82 and 84 are arranged in positions opposing (directly above)first platen 72 by operating robot arms 78 and 80, and as shown in FIG.3B, Cu film 52 and Cu seed film 50 are polished until Ta film 48 isexposed (the first polishing step). Next, wafer holding tables 82 and 84are arranged in positions opposing (directly above) second platens 74and 76 by operating robot arms 78 and 80, and as shown in FIG. 3C, Tafilm 48 is polished until thermal oxide film pattern 46 is exposed (thesecond polishing step).

[0066] A method of polishing the damascene interconnection layer (FIGS.3A-3C) in two steps (a first polishing step and a second polishing step)includes a method with a plurality of platens and the respective waferholding tables corresponding to the platens within one CMP apparatus, inaddition to the methods shown in FIGS. 5, 6 and 7. In this case, in afirst polishing step, a first wafer holding table sucks and holds awafer and polishing is performed using a polishing pad attached to acorresponding first platen. Thereafter, the wafer is transferred fromthe first holding table to a second holding table using a robot arm, anda second polishing step is performed using a polishing pad attached to asecond platen.

[0067] Other methods include a method with CMP apparatuses separatelyprovided to perform the first and second polishing steps. Still anothermethod may include a method using the same CMP apparatus and the sameplaten for the first and second polishing steps. In this case, the firstpolishing step is initially performed on a prescribed number (100, etc.)of wafers. The second polishing step is thereafter performed byreplacing the elastic member arranged under the polishing pad.

[0068] While the embodiments of the present invention have beendescribed above, the present invention is not limited to theseembodiments and may be changed within a scope of technical conceptsillustrated in the claims.

[0069] Industrial Applicability

[0070] In accordance with the present invention, since a material havinga hardness defined by JIS standard K6301 (A type) of 10-40 and athickness of 5-30 mm is used as an elastic member, both flatness anduniformity of a wafer can effectively be improved even if the wafer isheld by vacuum suction. Therefore, advantageously, an accurate damasceneinterconnection can be formed.

1. A chemical mechanical polishing apparatus planarizing a surface of a metal film formed on a semiconductor substrate (10), comprising: a substrate holding table (42) holding said semiconductor substrate by vacuum suction; a polishing pad (12) being in contact with said semiconductor substrate; a platen (36) holding said polishing pad; and an elastic member (16) arranged between said polishing pad and said platen, wherein said elastic member has a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm.
 2. A damascene interconnection forming apparatus forming an insulating film (46) on a semiconductor substrate (10), forming a recessed portion in a prescribed region of the insulating film, forming a barrier metal film (48) on a surface of the insulating film including the recessed portion, and forming a metal interconnection film (52) on said barrier metal film to completely fill in at least said recessed portion, followed by polishing said metal film and said barrier metal film until said insulating film is exposed in a region other than said recessed portion, comprising: first polishing means for performing a first polishing step of polishing said metal interconnection film until said barrier metal film is exposed in the region other than said recessed portion; and second polishing means for performing a second polishing step of polishing said barrier metal film until said insulating film is exposed in the region other than said recessed portion, wherein said first polishing means includes a substrate holding table holding said semiconductor substrate by vacuum suction, a polishing pad being in contact with said semiconductor substrate, a platen holding said polishing pad, and an elastic member arranged between said polishing pad and said platen and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, and said second polishing means includes a substrate holding table holding said semiconductor substrate by vacuum suction, a polishing pad being in contact with said semiconductor substrate, a platen holding said polishing pad, and an elastic member arranged between said polishing pad and said platen and having a hardness defined by JIS standard K6301 (A type) of at least
 50. 3. The damascene interconnection forming apparatus according to claim 2, wherein said first and second polishing means are included in a single chemical mechanical polishing apparatus, the polishing apparatus includes a substrate holding table (66) holding said semiconductor substrate (10) by vacuum suction, first and second platens (54, 56) each arranged in a position opposing said substrate holding table in a polishing operation, a first polishing pad (62) arranged on said first platen (54), a second polishing pad (64) arranged on said second platen (56), a first elastic member (58) arranged between said first platen and said first polishing pad and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, and a second elastic member (60) arranged between said second platen and said second polishing pad and having a hardness defined by JIS standard K6301 (A type) of at least 50, and in performing said first polishing step, polishing is performed using said first polishing pad by arranging said substrate holding table in a position opposing said first platen, and in performing said second polishing step, polishing is performed using said second polishing pad by arranging said substrate holding table in a position opposing said second platen.
 4. The damascene interconnection forming apparatus according to claim 3, wherein said chemical mechanical polishing apparatus includes one said first platen (54), a plurality of said second platens, and said substrate holding tables as many as said second platens (56).
 5. A damascene interconnection forming method of forming an insulating film (46) on a semiconductor substrate (10), forming a recessed portion in a prescribed region of the insulating film, forming a barrier metal film (48) on a surface of the insulating film including the recessed portion, and forming a metal interconnection film (52) on said barrier metal film to completely fill in at least said recessed portion, followed by polishing said metal film and said barrier metal film until said insulating film is exposed in a region other than said recessed portion, comprising: a first polishing step of polishing said metal interconnection film until said barrier metal film is exposed in the region other than said recessed portion using first polishing means; and a second polishing step of polishing said barrier metal film until said insulating film is exposed in the region other than said recessed portion using second polishing means, wherein said first polishing means includes a substrate holding table (66) holding said semiconductor substrate by vacuum suction, a polishing pad (62, 64) being in contact with said semiconductor substrate, a platen (54, 56) holding said polishing pad, and an elastic member (58, 60) arranged between said polishing pad and said platen and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, and said second polishing means includes a substrate holding table holding said semiconductor substrate by vacuum suction, a polishing pad being in contact with said semiconductor substrate, a platen holding said polishing pad, and an elastic member arranged between said polishing pad and said platen and having a hardness defined by JIS standard K6301 (A type) of at least
 50. 6. The damascene interconnection forming method according to claim 5, wherein said first and second polishing means are included in a single chemical mechanical polishing apparatus, the polishing apparatus includes a substrate holding table (66) holding said semiconductor substrate (10) by vacuum suction, first and second platens (54, 56) each arranged in a position opposing said substrate holding table in a polishing operation, a first polishing pad (62) arranged on said first platen (54), a second polishing pad (64) arranged on said second platen (56), a first elastic member (58) arranged between said first platen and said first polishing pad and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, and a second elastic member (60) arranged between said second platen and said second polishing pad and having a hardness defined by JIS standard K6301 (A type) of at least 50, and in performing said first polishing step, polishing is performed using said first polishing pad by arranging said substrate holding table in a position opposing said first platen, and in performing said second polishing step, polishing is performed using said second polishing pad by arranging said substrate holding table in a position opposing said second platen.
 7. The damascene interconnection forming method according to claim 6, wherein said chemical mechanical polishing apparatus includes one said first platen (54), a plurality of said second platens, and said substrate holding tables as many as said second platens (56). 